We have studied in search of useful derivatives of a known compound, forphenicine having the following structure: ##STR2## Forphenicine is a known substance which was first isolated from the culture broth of a strain of actinomycetes by H. Umezawa et al. and which is active as a strong inhibitor alkaline phosphatase and enhances delayed-type hypersensitivity and increases the number of antibody-forming cells (Japanese Patent Prepublication "Kokai" No. 116685/75, "Journal of Antibiotics" Vol. 31, No. 3, pp. 244-246 and Vol. 31, No. 5, pp. 483-484 (1978) as well as Vol. 30, Suppl. S-153 (1977)).
We have already discovered a useful derivative of forphenicine of the structural formula: ##STR3## This compound is designated as forphenicinol and is found to have an immunopotentiating activity (see Japanese Patent Pre-publication No. 44632/79 published on Apr. 9, 1979; and co-pending U.S. patent application Ser. No. 21,222, now U.S. Pat. No. 4,238,507.
In the course of our further studies, we have now found new related compounds of the general formula: ##STR4## and salts and hydrates thereof, wherein R represents hydrogen atom or a linear or branched lower alkyl group. These compounds have been observed to possess immunopotentiating activity and are thus useful as an immunopotentiator for enhancing the immune response in living animals and humans.
An object of this invention is to provide new compounds which exhibit immunopotentiating activities. Another object of the invention is to provide processes of producing these new, useful compounds. Further object of the invention is to provide an immunopotentiator or antitumor agent comprising these compounds.
Other objects and utilities of the invention will become apparent from the following descriptions.